This invention relates in general to apparatus for providing radiant energy in a relatively narrow wavelength band for the purpose of photo-curing materials such as photo-curable dental restoration material or compositions. The invention is more specifically directed to a low-power high-intensity curing lamp to be used in dental curing apparatus.
In the field of dentistry, there is a growing use of dental compositions, e.g., sealants, dental filling and restoration materials, dental impression materials, and other compounds, that rely on photoinitiators to react in the presence of light. Some of these materials cure, or harden, upon exposure to blueviolet light, specifically light between 400 and 500 nanometers in wavelength. The photoinitiators have a peak sensitivity in the vicinity of about 470 nm.
In order to treat a patient, the dentist can prepare the material under subdued light, or in the presence of red light, whose longer wavelengths do not bring about curing of the material to the patient's tooth or teeth, e.g. by filling a cavity. Under these conditions, the material remains workable, then the dentist applies intense blueviolet light for a period of time to cure the material to a hardened state.
A number of photo-curable dental materials are known and available, and several typical compositions are described in U.S. Pat. Nos. 4,504,231; 4,514,174; and 4,491,453.
In order to cure the material, the dentist may apply the intense blueviolet light using a hand-held light gun. These guns typically have an electric lamp device within a housing, and an elongated light conduit to carry the light to the material within the patient's mouth. The material typically can require 60 to 90 seconds of curing time, and during this time the tip of the light conduit is in close contact with the patient's mouth. It is quite important that the distal tip of the conduit remain cool, and that there not be great amounts of infrared which can disrupt the curing process and possibly heat the patient's teeth causing discomfort or damage.
Also, for reasons of operator safety, the lamp or gun must keep stray radiation within safe limits, and produce neither ionizing ultraviolet radiation nor infrared radiation in significant amounts.
In order to produce light of sufficient intensity within a bandwidth for effective curing, the currently available devices require a rather powerful lamp that also generates significant radiation outside the optimal 400-500 nm range. Typically, a heat filter is required in the optical path of the light emitted from the lamp to block or absorb long-wavelength radiation. Heat management is a problem for these devices, and provisions must be included to keep the lamp and its surroundings from overheating.
Previous dental curing apparatus for this general purpose are described in U.S. Pat. Nos. 4,229,658; 4,385,344; and 4,546,261.
So a need exists in the dental curing art to devise a lamp that can operate at low enough power inputs so that excessive heat is not generated and, yet, generate high enough light intensity in an optimum wavelength range for effective photo-curing of dental compositions. Or, equivalently, a lamp is required with a relatively high spectral efficiency for an optimum wavelength range specified.
In the lamp arts, it has been known that metal halide discharge lamps have provided improved efficiencies compared to incandescent and other types of lamps. In a typical metal halide lamp, an envelope of vitreous silica material defines an arc chamber which contains a fill of mercury, inert gas, and a metal halide additive. Sealed in the arc chamber is a pair of refractory tungsten electrodes having tips spaced apart from one another. After an arc discharge is established between the electrode tips, the temperature of the arc chamber rapidly increases, causing the mercury and metal halide additives to vaporize. The mercury atoms and metal atoms of the metal halide are ionized and excited, causing emissions of radiation at spectrums characteristic of the respective metals. This radiation is substantially combined within the arc chamber to produce a resultant light output having an established intensity and spectral characteristic.
A disadvantage experienced with metal halide lamps is that at low power input levels (i.e., 35 watts and below), improved efficiencies have not been generally attainable. In addition, at such low power input levels, the spectral characteristics of the light emitted from such low watt lamps have not been adequately controllable.
In a copending application, now U.S. Pat. No. 5,144,201 Feb. 23, 1990 by Timothy W. Graham and Daniel C. Briggs, entitled Low Watt Metal Halide Lamp, assigned to the same assignee as this application, useful and efficient low watt metal halide discharge lamps are disclosed. These lamps achieve, at input powers of 35 watts and below, efficiencies and spectral control that are suitable for the above-described dental curing applications. However, a set of parameters for these low watt metal halide lamps had to be developed and a halide additive or combination of additives needed to be found in order to produce a high intensity lamp output within the desired wavelength range for dental curing applications.